In a digital audio system, if a sampling data piece erroneously is made to have a level significantly different from the level of the true data piece, large noise is generated. Such noise is referred to as impulse noise. Impulse noise is significantly noticeable when it occurs for a sampling data piece having a small amplitude.
Conventionally, an impulse noise suppressing circuit has been used to remove such impulse noise. The impulse noise suppressing circuit monitors levels of respective sampling data pieces. If the level of given sampling data piece Dn is dominant to the levels of preceding and succeeding sampling data pieces Dn−1 and Dn+1, the sampling data piece Dn is judged to be impulse noise, and the preceding sampling data piece Dn−1 is substituted for the sampling data piece Dn.
The impulse noise suppressing circuit is in operation all the time. Accordingly, if a sampling data piece, a high frequency component, for example, other than impulse noise, that has a level dominant to preceding and succeeding sampling data pieces is applied to the impulse noise suppressing circuit, it will be mistaken for impulse noise, and sampling data substitution will be done. High frequency components, which are not impulse noise, are cut away, which degrade sound quality.
An object of the present invention is to provide an impulse noise suppressing apparatus which can reduce degradation of sound quality, while suppressing impulse noise.